The present invention relates to a color cathode ray tube, and relates, more particularly, to a color cathode ray tube capable of reducing displacement of beam landing attributable to deformation of a shadow mask or oscillation and capable of reducing howling of a phosphor screen, by setting in suitable conditions the curvature of an effective surface of the shadow mask and electron beam through hole rows formed by a plurality of electron beam through holes.
In general, a color cathode ray tube has a vacuum envelop composed of an almost rectangular panel 3 provided with a skirt 2 at the periphery of an effective portion 1 having a curved surface, and a funnel 4 connected to the skirt 2, as shown in FIG. 1. A phosphor screen 5 is provided on the inner surface of the effective portion 1 of the panel 3. At the inside of the phosphor screen 5, there is disposed an almost rectangular shadow mask 9, composed of a mask main body 7 having a large number of electron beam through holes or apertures on an effective surface 6 formed in an almost rectangular curved surface opposite to the phosphor screen, and an almost rectangular mask frame 8 fitted to the periphery of the mask main body 7. In the mean time, within a neck 11 of the funnel 4, there is disposed an electron gun assembly 13 for discharging three electron beams 12B, 12G and 12R. The three electron beams 12B, 12G and 12R emitted from this electron gun assembly 13 are deflected by a magnetic field generated from a deflector 14 mounted on the outside of the funnel 4. These three electron beams 12B, 12G and 12R are then selected by the shadow mask 9 and are directed to the phosphor screen 5. When the phosphor screen 5 is scanned both horizontally and vertically by the three electron beams 12B, 12G and 12R, a color image is displayed on the phosphor screen 5.
In this color cathode ray tube, the holes or apertures formed on the effective surface 6 of the shadow mask 9, through which the electron beams pass, are arranged as follows. A plurality of electron beam through holes are laid out in one line along a short axis (Y axis) direction of the shadow mask, and a plurality of these electron beam through hole array or aperture array composed of the plurality of electron beam through holes in the short axis direction are arranged in a long axis (X axis) direction of the shadow mask. Corresponding to this arrangement of the electron beam through holes, the phosphor screen 5 is structured by black strip layers, i.e., non-light emitting layers extending in the short axis direction, and three-color phosphor layers buried between the black non-light emitting layers. The color cathode ray tube having this structure is called an in-line type, and has been in practical use.
Generally, in order to achieve a display of an image without any color purity degradation on the phosphor screen of a color cathode ray tube, it is essential that each of the three electron beams passing through the electron beam through holes of the shadow mask makes a correct landing on the three color phosphor layer of the phosphor screen. In order to perform a correct landing of the three electron beams, it is necessary that a distance (q value) between the inner surface of the effective portion of the panel and the effective surface of the shadow mask is set at a value within a predetermined permissible range.
In recent years, in order to improve the visibility of an image, color cathode ray tubes have been designed to have a flat surface or almost a flat surface, with a smaller curvature, for the external surface of the effective portion of the panel. These color cathode ray tubes need to have a smaller curvature for the internal surface of the effective portion of the panel, for obtaining good visibility of an image and from the viewpoint of forming the panel. In this case, the effective surface of the shadow mask needs to have a small curvature corresponding to the curvature of the internal surface of the effective portion of the panel, in order to obtain a suitable distance from the internal surface of the effective portion of the panel.
However, the reduction in the curvature of the effective surface of the shadow mask involves such risks that the strength of the curved surface becomes weak, that a local deformation occurs in the shadow mask and the color cathode ray tube at the manufacturing stage, and that color purity is deteriorated. Further, when the color cathode ray tube is built into the image receiver, a howling occurs by the sound from the speaker, which lowers the color purity.
On the other hand, if the curvature of the effective surface of the shadow mask is set large in an attempt to prevent deterioration of the color purity attributable deformation or oscillation of the shadow mask, and if the curvature of the internal surface of the effective portion of the panel is set to correspond to this curvature of the effective surface, then the curvature of the internal surface becomes larger for the shape of the external surface of the effective portion. This not only makes it difficult to form the panel, but also has a risk of a reduction in the visual field angle due to a total reflection and a deterioration in the visibility due to a reflected image on the internal surface of the panel.
There has already been made a proposal for preventing the deterioration of color purity attributable to deformation or oscillation of the shadow mask. According to this proposal, as shown in FIG. 2, the internal surface of an effective portion 1 of a panel 3 has a curvature in its short axis direction, and a radius of curvature in the long axis direction is set as infinite in its long axis direction from the center to an intermediate portion of the panel. The radius of curvature in the long axis direction near the periphery of the short side is formed in a larger curved surface than the radius of curvature in the long axis direction from the center to the intermediate portion. The effective surface of the shadow mask is formed in a similar curved surface corresponding to the internal surface shape of the effective portion 1 of the panel 3.
When the effective portion 1 of the panel 3 and the effective surface of the shadow mask are set in the curved shapes as explained above, it becomes possible to improve the strength of the curved surface of the shadow mask 9 and to increase the atmospheric pressure strength of the vacuum envelop at the same time. However, even in this, the curved surface strength of the shadow mask 9 is insufficient at portions near the center of the effective surface 6. Further, the phosphor screen formed on the internal surface of the effective portion 1 of the panel 3 is degraded.
In general, the phosphor screen of the color cathode ray tube is formed based on a photo-lithographic method, according to which the black non-light emitting layer is formed first and then the three-color phosphor layer is formed, for the phosphor screen that is composed of the non-light emitting layer and the three-color phosphor explained above.
According to this photo-lithographic method, at first, a photosensitive material is coated on the internal surface of an effective portion 1 of a panel 3, to form a photosensitive film 15, as shown in FIG. 3A. This photosensitive film 15 is exposed by utilizing a shadow mask 9. After the photosensitive mask 15 has been developed, a resist 17 in a striped pattern corresponding to an electron beam through hole 16 of the shadow mask shown in FIG. 3A, is formed as shown in FIG. 3B. Then, a black non-light emitting coating is coated on the internal surface of the effective portion 1 of the panel 3 on which the resist 17 has been formed. Thereafter, the coating is dried, and a black non-light emitting coated layer 18 is formed, as shown in FIG. 3C. After that, the black non-light emitting coated layer on the resist 17 is separated together with the resist 17, and a striped black non-light emitting layer 19 is formed, as shown in FIG. 3D.
Thereafter, a photosensitive phosphor slurry containing a phosphor and a photosensitive agent as main components is coated on the internal surface of the effective portion 1 of the panel 3 formed with the black non-light emitting layer 19, as shown in FIG. 3E. Then, this slurry is dried and a photosensitive phosphor slurry layer 21 is formed. This photosensitive phosphor slurry layer 21 is exposed similarly by utilizing the shadow mask 9 and is then developed. As a result, a striped blue phosphor layer 22B, for example, is formed in the striped space between the black non-light emitting layers 19, as shown in FIG. 3F. Thereafter, this method of forming a phosphor layer is repeated, and three-color phosphor layers 22B, 22G and 22R are formed in the striped space between the black non-light emitting layers 19, as shown in FIG. 3G.
For exposing the photosensitive film 15 and the photosensitive phosphor slurry layer 21, there are used the striped black non-light emitting layers 19 and a long light source which is long in the longitudinal direction of the phosphor layers 22B, 22G and 22R. This long light source having such a large length is used because a miss-landing of the electron beams in the longitudinal direction of the phosphor layers 22B, 22G and 22R does not affect the color purity in the in-line type color cathode ray tube. Therefore, it is not necessary to strictly approximate the light rays emitted from the light source to the locus of the electron beams emitted from the electron gun assembly. Moreover, the use of the long light source has such advantages that the exposure time can be reduced by an increased intensity of light beams emitted from the light source, and that it is possible to form the striped black non-light emitting layer 19 and the phosphor layers 22B, 22G and 22R, easily and continuously, without any break due to a bridge between the electron beam through holes.
However, if the above-described long light source is used, the panel 3 with the internal surface of the effective portion 1 having the curvature practically in only the short axis direction, with the curvature in the long axis direction almost infinite from the center to the intermediate portion in the long axis direction as shown in FIG. 2, has a problem that the longitudinal direction of a long light source 24 does not coincide with the longitudinal direction of a pattern 26 of one electron beam through hole 16 of the shadow mask 9 projected onto the internal surface of the effective portion 1 of the panel 3, as shown in FIG. 4A. Accordingly, as shown in FIG. 4B, there arises a displacement of xcex941 in the long axis direction at both ends 29a and 29b of the pattern 26 to which light beams 28a and 28b reach from both ends 27a and 27b of the long light source 24. This displacement xcex941 becomes a maximum at the intermediate portion of the long side of the effective portion 1.
Accordingly, as shown in FIGS. 5A and 5B, the black non-light emitting layers 19 and the phosphor layers 22B, 22G and 22R formed at the center of the effective portion 1 of the panel 3 form a normal stripe. However, the black non-light emitting layer 19 and the phosphor layers 22B, 22G and 22R make a zigzag shape at the intermediate portion in the long axis direction of the effective portion 1, which lowers the distinction or clearness of the phosphor screen near the intermediate portion of the long side and degrades the quality of the screen, as shown in FIG. 5C.
In order to prevent this degrading of the phosphor screen, there has been a conventional method according to which the internal surface of the effective portion of the panel is not exposed at the same time, but a shutter provided with apertures for partially exposing between the panel and the long light source is movably disposed, and in synchronism with the move of the shutter, the internal surface of the effective portion is exposed by slanting the long light source to make the longitudinal direction of the long light source coincide with the longitudinal direction of the pattern of the electron beam through holes of the shadow mask projected to the internal surface of the effective portion of the panel.
This exposure method, however, involves a complex structure of an exposing apparatus and requires a long exposure time as well.
Accordingly, there has recently been employed an exposure method according to which an optical lens is disposed on the long light source, and the locus of the light beam from the long light source is adjusted with this optical lens to carry out a simultaneous exposure of the internal surface of the effective portion of the panel.
However, this exposure method has a problem that in most cases it is not possible to sufficiently adjust the zigzag of the black non-light emitting layer and the phosphor layer.
In order to solve this zigzag of the black non-light emitting layer and the phosphor screen, there has been proposed a method in Jpn. Pat. Appln. KOKAI Publication No. 8-162034 (the corresponding U.S. application thereof matured into U.S. Pat. No. 5,672,934 (Ohama et al.) on Sep. 30, 1997). As shown in FIG. 6A and FIG. 6B, it is proposed that the electron beam through holes 16 of the shadow mask 9 has such a shape on the long side of the effective surface 6 that, in the area from the short side to a position apart from the short side at a distance of xc2xc width of the effective surface, the width being defined as a distance between the short sides, the slope is the largest at the end of the long side of the electron through holes in a direction to approach the short axis from the end of the opposite long side, and in the area inside ⅓ of the short axis distance (long axis side) from the long side, the slope angle xcex8 becomes larger in a direction away from the short axis and this slope angle is decreased or inverted to a minimum towards the short axis.
This shadow mask 9 is effective if the external surface of the panel has a curvature of about 2R. However, if the external surface of the panel is almost flat, there is a problem that the strength of the curved surface is reduced in the case where the distance between the internal surface of the effective portion of the panel and the effective surface 6 of the shadow mask 9 is set so as to have a suitable disposition of the stripe black non-light emitting layer and the phosphor layer.
As explained above, when the curvature of the external surface of the effective portion of the panel is decreased to have a flat surface or an almost a flat surface in an attempt to improve the visibility of an image, it is necessary to decrease the curvature of the internal surface of the effective portion of the panel. Along with this reduction, it is also necessary to decrease the curvature of the effective surface of the shadow mask. However, the reduction in the curvature of the effective surface of the shadow mask brings about the lowering of the strength of the curved surface, a local deformation of the shadow mask or the color cathode ray tube at a manufacturing stage, an oscillation due to a sound from the speaker when the color cathode ray tube has been built into the image receiver, resulting in the lowering of the color purity.
In order to prevent the lowering of the color purity attributable to deformation or oscillation of the shadow mask, there has been a proposal that the internal surface of the effective portion of the panel has a curvature in the short axis direction, and has almost a limitless radius of curvature in the long axis direction from the center to the intermediate portion in the long axis direction so that the radius of curvature in the long axis direction near the periphery of the short side is formed in a curved surface larger than the radius of curvature in the long axis direction from the center toward the intermediate portion, and that the effective surface of the shadow mask is formed to have a similar curved shape. However, even with this structure, the strength of the curved surface near the center of the effective surface of the shadow mask becomes insufficient. Further, this structure has a risk of causing a zigzag of the striped black non-light emitting layer and the three-color phosphor layer of the phosphor screen formed on the internal surface of the effective surface of the panel, and degrading the quality of the phosphor screen.
In order to prevent the zigzag of the black non-light emitting layer and the phosphor layer, there has also been proposed that, on the long side of the effective surface, in the area between a position with a distance of xc2xc of the short side distance from the short side and the short side, the slope is the largest at the end of the long side of the electron beam through holes toward the short axis from the end of the opposite side, and in the inside area (long axis side) with a distance of ⅓ of the short side distance from the long side, this slope angle xcex8 becomes larger in a direction away from the short axis, and the slope angle is decreased or is inverted to a minimum in a direction toward the short side. However, even with this structure, if the external surface of the panel is almost flat, there is a problem that the strength of the curved surface is reduced in the case where the distance between the internal surface of the effective portion of the panel and the effective surface of the shadow mask is set so as to have a suitable disposition of the stripe black non-light emitting layer and the phosphor layer.
It is an object of the present invention to provide a color cathode ray tube capable of reducing displacement of beam landing attributable to deformation of a shadow mask or oscillation due to a sound from a speaker, and capable of reducing howling of a phosphor screen attributable to zigzag of a striped black non-light emitting layer and a phosphor layer, by setting in suitable conditions the curvature of an effective surface of the shadow mask and electron beam through hole rows formed by a plurality of electron beam through holes.
According to the present invention, there is provided a color cathode ray tube, comprising: an almost rectangular panel having a flat surface or having a slight curvature on its external surface; a phosphor screen formed on an internal surface of an effective portion of the panel; a mask main body, having an almost rectangular shadow mask disposed opposite to the phosphor screen, with a plurality of electron beam through holes being disposed in one line in a short axis direction of the shadow mask on an effective surface of an almost rectangular curved shape opposite to the phosphor screen, and with this electron beam through hole line formed by the plurality of electron beam through holes being laid out by a plurality of number in a long axis direction of the shadow mask; and an almost rectangular mask frame fitted to the periphery of the mask main body, wherein the shadow mask is structured such that the layout distance between the adjacent electron beam through holes near the long side of the effective surface is larger than the layout distance between the adjacent electron beam through holes at the center of the effective surface near the short axis of the shadow mask, and this layout distance becomes gradually smaller in a direction away from the short axis, and increases thereafter, and at a position near the short side of the effective surface, the layout distance becomes equal to or larger than the layout distance near the short axis.
In the color cathode ray tube, the effective surface of the shadow mask is structured such that the effective surface has a curvature in the short axis direction, and in an area between a position with a ⅓ distance of the short side distance in the long axis direction from the short axis and the short axis, the curvature in the short axis direction is a maximum near the short axis and the curvature becomes gradually smaller in a direction away from the short axis.
Further, according to the present invention, there is provided a color cathode ray tube, comprising: an almost rectangular panel; a phosphor screen formed on an internal surface of an effective portion of the panel; a mask main body, having an almost rectangular shadow mask disposed opposite to the phosphor screen, with a plurality of electron beam through holes being disposed in one line in a short axis direction of the shadow mask on an effective surface of an almost rectangular curved shape opposite to the phosphor screen, and with this electron beam through hole line formed by the plurality of electron beam through holes being laid out by a plurality of number in a long axis direction of the shadow mask; and an almost rectangular mask frame fitted to the periphery of the mask main body, wherein the shadow mask is structured such that the layout distance of the electron beam through hole array on the long axis increases gradually in a direction away from the short axis, and at a position near the long side of the effective surface, the layout distance becomes smaller at an intermediate portion in the long axis direction near the short axis.
Further, according to the present invention, there is provided a color cathode ray tube, comprising: an almost rectangular panel having a flat surface or having a slight curvature on its external surface; a phosphor screen formed on an internal surface of an effective portion of the panel; a mask main body, having an almost rectangular shadow mask disposed opposite to the phosphor screen, with a plurality of electron beam through holes being disposed in one line in a short axis direction of the shadow mask on an effective surface of an almost rectangular curved shape opposite to the phosphor screen, and with this electron beam through hole line formed by the plurality of electron beam through holes being laid out by a plurality of number in a long axis direction of the shadow mask; and an almost rectangular mask frame fitted to the periphery of the mask main body, wherein the shadow mask is structured such that the layout distance of the electron beam through hole array on the long axis increases gradually in a direction away from the short axis, and at a position near the long side of the effective surface, the layout distance becomes smaller at an intermediate portion in the long axis direction near the short axis.
Further, according to the present invention, there is provided a color cathode ray tube, comprising: an almost rectangular panel having a flat surface or having a slight curvature on its external surface; a phosphor screen formed on an internal surface of an effective portion of the panel; a mask main body, having an almost rectangular shadow mask disposed opposite to the phosphor screen, with a plurality of electron beam through holes being disposed in one line in a short axis direction of the shadow mask on an effective surface of an almost rectangular curved shape opposite to the phosphor screen, and with this electron beam through hole line formed by the plurality of electron beam through holes being laid out by a plurality of number in a long axis direction of the shadow mask; and an almost rectangular mask frame fitted to the periphery of the mask main body, wherein the shadow mask is structured such that, at a position near the short axis, the slope of the electron beam through hole array near the long side of the effective surface has a slope closer to the short axis at the end of the long axis side as compared with the slope at the end of the opposite side of the electron beam through holes, and the angle of this slope gradually reduces in a direction away from the short axis, and the electron beam through hole array have an inverse slope in an area between a position with a ⅓ distance of the short side distance from the short side of the effective surface and the short side, and thereafter the angle of this inverse slope increases in a direction toward the short side.
Further, according to the present invention, there is provided a color cathode ray tube, comprising: an almost rectangular panel; a phosphor screen formed on an internal surface of an effective portion of the panel; a mask main body, having an almost rectangular shadow mask disposed opposite to the phosphor screen, with a plurality of electron beam through holes being disposed in one line in a short axis direction of the shadow mask on an effective surface of an almost rectangular curved shape opposite to the phosphor screen, and with this electron beam through hole line formed by the plurality of electron beam through holes being laid out by a plurality of number in a long axis direction of the shadow mask; and an almost rectangular mask frame fitted to the periphery of the mask main body, wherein the shadow mask is structured such that, at a position near the short axis, the slope of the electron beam through hole array near the long side of the effective surface has a slope closer to the short axis at the end of the long axis side as compared with the slope at the end of the opposite side of the electron beam through holes, and the angle of this slope gradually reduces in a direction away from the short axis, and the electron beam through hole array have an inverse slope in an area between a position with a ⅓ distance of the short side distance from the short side of the effective surface and the short side, and thereafter the angle of this inverse slope increases in a direction toward the short side.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.